论文标题
MEG II实验的漂移室
The Drift Chamber of the MEG II experiment
论文作者
论文摘要
Paul Scherrer Institut的MEG实验搜索了带电的Lepton-Fravory-violation Mu+ - > e+ gamma衰变。 MEG已经为分支比率设定了世界上最佳的上限：BR <4.2x10^-13 @ 90％C.L.对整个检测器的升级（MEG II）已被批准，以获得敏感性的实质性提高。目前，MEG II正在完成各种探测器的升级，工程运行和委托前进行的跑步，在2018年和2019年进行。新的Potitron Tracker是一个独特的，具有高粒状的超轻型圆柱漂移室（CDCH），具有高粒状：具有高粒状：9层的192正方形漂移细胞，配置9层，〜6-9mmmmm宽的插入式，一组成熟，〜12000 nigress a 〜12000 nigress a 〜12000 nigress a 〜12000 nigress，〜12000 nigress a 〜12000。为了确保漂移电池的静电稳定性，应由于高电线密度（12线/cm^2）而制定新的接线策略，对电线位置和电线机械张力的均匀性（大于0.5 g）的严格精确要求（基本思想）是通过焊接（16或32）厚的电线（16或32）厚的电线来创建多击框架。多线框架和窥视垫圈沿半径交替重叠，以设置适当的单元宽度，该细胞宽度在由舵式车轮形端板的辐条定义的十二个扇区中的每个扇区中。尽管组装策略的概念简单性，但根据设定要求，多线框架的构建却强加了自动接线系统。 MEG II CDCH是有史以来第一个以模块化方式设计和建造的圆柱漂移室，它将允许跟踪正上音，动量大于45 meV/c，并通过使用很少的材料（1.5x10^-3 x0）具有高效率。我们描述了CDCH设计和构造，INFN-LECCE的接线阶段，电线的选择，其机械性能，INFN-PISA和调试的组装和密封。
The MEG experiment at the Paul Scherrer Institut searches for the charged-Lepton-Flavor-Violating mu+ -> e+ gamma decay. MEG has already set the world best upper limit on the branching ratio: BR<4.2x10^-13 @ 90% C.l. An upgrade (MEG II) of the whole detector has been approved to obtain a substantial increase of sensitivity. Currently MEG II is completing the upgrade of the various detectors, an engineering run and a pre-commissioning run were carried out during 2018 and 2019. The new positron tracker is a unique volume, ultra-light He based cylindrical drift chamber (CDCH), with high granularity: 9 layers of 192 square drift cells, ~6-9 mm wide, consist of ~12000 wires in a full stereo configuration. To ensure the electrostatic stability of the drift cells a new wiring strategy should be developed due to the high wire density (12 wires/cm^2 ), the stringent precision requirements on the wire position and uniformity of the wire mechanical tension (better than 0.5 g) The basic idea is to create multiwire frames, by soldering a set of (16 or 32) wires on 40 um thick custom wire-PCBs. Multiwire frames and PEEK spacers are overlapped alternately along the radius, to set the proper cell width, in each of the twelve sectors defined by the spokes of the rudder wheel shaped end-plates. Despite to the conceptual simplicity of the assembling strategies, the building of the multiwire frames, with the set requirements, imposes a use of an automatic wiring system. The MEG II CDCH is the first cylindrical drift chamber ever designed and built in a modular way and it will allow to track positrons, with a momentum greater than 45 MeV/c, with high efficiency by using a very small amount of material, 1.5x10^-3 X0 . We describe the CDCH design and construction, the wiring phase at INFN-Lecce, the choice of the wires, their mechanical properties, the assembly and sealing at INFN-Pisa and the commissioning.
